Megamasers

Ylva Pihlström

University of New Mexico

What are megamasers?

• Luminous, extragalactic masers with Lmegamaser > 106 Lgalactic maser

• Detected species: SiO, CH, H2CO, OH and H2O

• Associated with nuclear regions of active galaxies• Probes of high density regions

• OH pumped by IR photons, H2O by collisions

Van Loon et al. 96; Whiteoak et al. 80; Baan et al. 86; Araya et al. 04Van Loon et al. 96; Whiteoak et al. 80; Baan et al. 86; Araya et al. 04

OH megamasers: history

• First detected in Arp220• Association with host galaxy IR color• Surveys of IRAS galaxies

• Detection rates high for high LFIR

Associated with nuclear regions of galaxies, in particular starburst nuclei of major mergers -

ULIRGs.

Baan et al. 82Baan et al. 82

Henkel et al. 86Henkel et al. 86

Stavely-Smith 87, 92; Norris et al. 89Stavely-Smith 87, 92; Norris et al. 89

Baan 89; Darling & Giovanelli 02Baan 89; Darling & Giovanelli 02

Sturm et al 96; Baan & Klöckner 06Vignali et al. 05 Sturm et al 96; Baan & Klöckner 06Vignali et al. 05

1667 MHz OH

1665 MHz OH

Tracers of mergers

• Strong starburst/merger association

• The OH 18cm lines favors dusty environments

• Trace merger rate over cosmic time

• Could help discriminating between different evolutionary scenarios

Darling & Giovanelli 02Darling & Giovanelli 02

Physical conditions

• Detected in several lines (mainly 1667 and 1665 MHz lines)

• Large supply of infrared photons

=> Inversion by infrared photons

Baan 85; Norris 95; Henkel et al. 87; Burdyuzha & Vikulov 90; Randell et al. 95Baan 85; Norris 95; Henkel et al. 87; Burdyuzha & Vikulov 90; Randell et al. 95

Skinner et al. 97Skinner et al. 97

Radio - IR correlation + LOH L60:

Standard model with unsaturated maser emission amplifying nuclear continuum background.

Baan 85; Henkel & Wilson 90Baan 85; Henkel & Wilson 90

OH megamasers with interferometers

Interferometric studies indicate molecular tori associated with massive central engines (Mrk231, IIIZw35, Mrk273, IC694)

Polatidis et al. 04; Klöckner et al. 03; Pihlström et al. 01; Richards et al. 06Polatidis et al. 04; Klöckner et al. 03; Pihlström et al. 01; Richards et al. 06

Klöckner et al. 03Klöckner et al. 03

At VLBI resolution

• Starburst related radio continuum resolved out

• Masers in compact regions, large line widths (Arp220, IIIZw35)

• Consistent with variability studies, indicating maser sizes <1.2pc (IRAS12032+1707)

Lonsdale et al. 98; Diamond et al. 99Lonsdale et al. 98; Diamond et al. 99

IIIZw35

Darling & Giovanelli 02Darling & Giovanelli 02

Possible explanations

• Clumpy torus model, resulting in different emission spectra as compared to a smooth medium

Parra et al. 05Parra et al. 05

New observations of Arp220

• Inverted gas local and associated with the radio supernova

• Adds to the standard model

Lonsdale, Bialecki, Diamond in prep.Lonsdale, Bialecki, Diamond in prep.

Lonsdale et al. 06Lonsdale et al. 06

• 50 compact continuum sources (RSNe): 25% have associated bright, wide maser emission, also OH absorption.

H2O megamasers: history

• First detected in NGC4945• Circinus• NGC3079 • NGC1068, NGC4258

• Interferometric observations of NGC1068 and NGC4258 • Survey

Associated with nuclear regions of galaxies, and in particular Seyfert 2s and LINERs.

Dos Santos & Lepine 79Dos Santos & Lepine 79

Gardner & Whiteoak 82Gardner & Whiteoak 82

Henkel et al. 84; Haschick & Baan 85Henkel et al. 84; Haschick & Baan 85

Claussen et al. 84Claussen et al. 84

Claussen & Lo 86; Claussen et al. 88; Haschick et al. 90Claussen & Lo 86; Claussen et al. 88; Haschick et al. 90

Braatz et al. 94, 96, 97Braatz et al. 94, 96, 97

H2O megamasers: types

• Circumnuclear AGN disks - e.g. NGC4258

• Associated with radio jets - e.g. NGC1052 and Mrk348

Nakai et al. 93; Haschick & Baan 90; Haschick et al. 94; Greenhill et al. 95Nakai et al. 93; Haschick & Baan 90; Haschick et al. 94; Greenhill et al. 95

Claussen et al. 98; Peck et al. 01Claussen et al. 98; Peck et al. 01

• Other types: kilomasers - e.g. M51, M82, NGC253 and NGC2146

Ho et al. 87; Henkel et al. 84, 88; Claussen et al. 84, Tarchi et al. 02Ho et al. 87; Henkel et al. 84, 88; Claussen et al. 84, Tarchi et al. 02

Jet-driven megamasers

• NGC1068 in jet-bending region (Gallimore et al. 96, 01)

• NGC1052 along the SW jet (Claussen et al. 98)

• Mrk348 toward the northern jet (Peck et al. 03)

Mrk348Mrk348

Mrk348• Broad line (130 km/s) on < 0.3 pc,

rapid variability => masers from shocked

region

• Temporal correlation between maser and continuum flux density suggest common origin

• Spectra of jet-driven masers differs significantly from disk-masers

Peck et al. 03Peck et al. 03

Accretion disk H2O megamasers

NGC4258

M=39x106 MS

Miyoshi et al. 1994Miyoshi et al. 1994

NGC1068

M=15x106 MS

Greenhill & Gwinn 97Greenhill & Gwinn 97 Greenhill et al. 03Greenhill et al. 03

Circinus

M=1.7x106 MS

Can be used to estimate black hole masses:

Test AGN unified schemes• Associated with obscuring column densities in Type 2 AGN

• Type 2 AGN not well understood? Is the obscuring torus really a torus?

• Warped accretion disks and outflows could be candidates for obscuring structures

CircinusGreenhill et al. 03; Herrnstein et al. 97Greenhill et al. 03; Herrnstein et al. 97

Extragalactic distance scale (EDS)Impacts cosmological key questions

• Estimates of equation of state for dark energy requires constraints on expansion rate

• Requires H0/H0 < 1% today > 10%

• Most robust estimate: 889 Cepheids in 31 galaxies within 30 Mpc (PL relation in the LMC).

Freedman et al. 01Freedman et al. 01

Hu 05Hu 05

Geometric distances

• Estimates of H0 directly via geometric distances should be more robust

• Tie the EDS to galaxies with geometric distances– Broad Vrecession range

• Obtained from water megamasers– VLBI mapping– Constrained geometry, high accuracy modeling

D

vv

r

rotlos θ

2

=&D

vrotx =θ&Acceleration distanceAcceleration distance Proper motion distanceProper motion distance

Uncertainty progress NGC4258

Error Component Type Comparison with Herrnstein et al. 99

0.03 Mpc Statistical Reduction by factor 6

0.3 Mpc Disk Model

Systematic

Work in progress: identifying all sources of modeling systematics

0.1 Mpc Eccentricity Systematic

Investigation of e ≤ 0.1 space -> uncertainty reduced by factor 4

7.2 ±0.03 ±0.3 ±0.1 Mpc (4%)

Humphreys et al. 06Humphreys et al. 06Acceleration fitting using 51 epochs of data, uses a 12 parameter 3D 2 fitting model.

Towards 1% accuracy in H0

• NGC4258: VLBI, HST (Cepheids) H0/H0 ~ a few %

• Tie the EDS to maser galaxies:

Individual D/D ~ a few to 20%

N galaxies H0/H0 ~ (D/D)N-0.5

N~10 with the VLBA in 2010, SKA could increase N substantially (100-1000, Morganti 04).

N~10 with the VLBA in 2010, SKA could increase N substantially (100-1000, Morganti 04).

New H2O megamaser• 183 GHz megamasers

detected in Arp220, in the 31,3-22,0 line.

• [A weaker detected in NGC3079]

• 350 km/s, probably starburst associated

Cernicharo et al. 06Cernicharo et al. 06

Humphreys et al. 05Humphreys et al. 05

Extragalactic masers: future• Megamasers occur in nuclei of active galaxies - need VLBI.

• OH: Even though most emission is in 100 pc scale tori, what about the compact spots with large line widths?

• Why don't we see OH megamasers in every ULIRG? Can we use them as tracers of the merger rate as a function of z?

• H2O: Look forward to more geometric distances!

• What about the kilomasers - to date largely unexplored. Also includes 'outsider' masers.

Spitzer and SMA data might help out!Spitzer and SMA data might help out!

Lonsdale et al.; Parra et al.Lonsdale et al.; Parra et al.

Hagiwara et al. 01, Henkel et al. 06; Braatz et al. 04; Greenhill et al. 02; Nagar et al. 02; Tarchi et al. 03Hagiwara et al. 01, Henkel et al. 06; Braatz et al. 04; Greenhill et al. 02; Nagar et al. 02; Tarchi et al. 03